High voltage electric circuit-breakers of the air-breakers type



April 18, 1961 D. LEGG ETAL 2,930,781

HIGH VOLTAGE ELECTRIC CIRCUIT-BREAKERS OF THE AIR-BREAKERS TYPE 2 Sheets-Sheet 1 Filed March 10, 1955 u lulla Apnl 18, 1961 LEGG 2,980,781

HIGH VOLTAGE ELECTRIC CIRCUIT-BREAKERS OF THE AIR-BREAKERS TYPE Filed March 10, 1955 2 Sheets-Sheet 2 G E mm. m s V m T m Q VWN mam M W w United States Patent HIGH VOLTAGE ELECTRIC CIRCUIT-BREAKERS OF THE AIR-BREAKERS TYPE Duncan Legg, South Shields, and Austin Frederick Brabant Young, Kenton, Newcastle-on-Tyne, England, assignors to A. Reyrolle & Company Limited, Hebburn, England, a company of Great Britain Filed Mar. 10, 1955, Ser. No. 493,422

Claims priority, application Great Britain Mar. 16, 1954 4 Claims. (Cl. 200144) This invention relates to high-voltage circuit-breakers of the air-break type, in which an arc is initiated in air between separable contacts and is transferred into at least one are chute where it is lengthened and cooled.

According to the present invention a porous or finely perforated barrier of electrical insulating material is situated in the arc chute and means are provided for producing a current of air moving transversely to the length of the arc and passing through the barrier to carry the are into the chute and hold it against the upstream surface of the barrier. No auxiliary magnet means such as blow-out coils or iron plates need be employed for assisting the arc transfer.

In air-break circuit-breakers, it is known to use a high-pressure air blast which is directed transversely to the line joining the separable contacts along which the arc is initially drawn, so as to transfer the are into an arc chute in which it is lengthened by being bowed into a series of transverse recesses or cells under the action of the air blast flowing into the cells. In this arrangement, however, the bowed portions of the are extending into the cells are subjected to an axial air blast, that is to say to a blast along the length of the arc. Such axial'blast action gives the circuit-breaker a very rapid de-ionising characteristic but at the same time makes it very prone to produce current-chopping, that is, the forced interruption of an alternating current at a point in the cycle other than a normal current zero, with wellknown attendant disadvantages.

The present invention, by enabling axial air blast along the arc to be avoided, reduces considerably the liability to current chopping.

The invention may be applied to a circuit-breaker having only a single arc chute or alternatively several arc chute chambers may be arranged in series.

In one arrangement the invention is applied to a circult-breaker having several arc chute chambers arranged radially but in helical disposition around the axis of a central passage in which the arc is initially drawn, the chambers communicating with one another to provide an elongated helical path into which the arc is driven by the radial flow of air outwardly from the central passage.

The invention may be carried into practice in various ways, but two specific embodiments will now be described by way of example with reference to the accompanying drawings, in which Figure l is a diagram illustrating in longitudinal section a circuit-breaker having a fish-tail-shaped are chute;

Figure 2 is a longitudinal section of a circuit-breaker having an arc chute comprising a stack of apertured discs;

Figure 3 is an exploded perspective view of four of the discs of the assembly of Figure 2 in their correct orientation, and

Figure 4 is a perspective view showing the four discs of Figure 3 assembled together to form part of the stack.

In the embodiment of Figure l a high-voltage circuitbreaker is provided with a fixed contact 19 and an axially aligned and axially withdrawable moving contact 11, the circuit-breaker terminals (not shown) being electrically connected to the two contacts and means being provided for separating the contacts to draw an arc between them on operation of the circuit-breaker. Associated with the contacts 10 and 11 is an arc chute structure 12 of fish-tail shape, near the root of which the contacts are located. The body 13 of the arc chute is formed of insulating material and is of flattened form enclosing an internal space 15 which is shallow in comparison with its width along its longitudinal axis. Near the narrow end of the body 13 are mounted the two contacts 10 and 11 with their axis of separation, indicated by the arrow 14, lying transverse to the longitudinal axis of the chute. Arc runners 16 and 17 of electrically conducting material are associated electrically with the two contacts and the two runners 16 and 17 extend in a divergent manner along the diverging side walls of the arc chute body 13. At the wide end of the chute remote from the contacts a porous insulating barrier 13 extends over the whole cross-section of the chute interior 15 transverse to the longitudinal axis of the chute body 13.

A duct 20 for compressed air is connected to the narrow end of the arc chute body 13 and delivers a flow of compressed air from'a reservoir or other source into the chute interior 15 across the initial arc zone between the contacts 10 and 11 and in a direction generally transverse to the axis of separation 14 of the contacts and generally parallel to the longitudinal axis of the arc chute. Means is provided for controlling the supply of air through the duct 20, and guide vanes 21 mounted in the throat of the arc chute body 13 direct the air blast over the whole cross-section of the chute.

In operation, when the circuit-breaker is tripped a blast of air flows through the duct 20 and thence through the chute interior 15, the air escaping outwardly through the porous barrier 18. The size of the air duct 20 is such, in proportion to the size of the chute body 13 and the porosity of the barrier 18, that the air pressure in the chute interior 15 builds up to a value favourable for are extinction. When the air flow and pressure are established in the chute the movable contact'11 is withdrawn to draw an are between the contacts 10 and 11, as indicated at 1. The arc is transferred to the arc runners 16 and 17 as indicated at 2, and is then driven by the air flow towards the wide end of the arc chute, the are being thus lengthened but remaining generally transverse to the air flow.

When the arc reaches the end of the chute it is held in the position 3 by the air flow against the inner surface of the porous barrier 18, the air flow being entirely transverse to the length of the arc. In this position heat is extracted from the arc by its intimate contact with the porous barrier 18 and with the side walls of the chute body 13 which are very close together in the region of the barrier. In addition some heat is withdrawn from the are by the air stream. The barrier 18 is sufliciently porous to allow a sufiicient air flow to keep the arc in the position 3 against it, whilst yet preventing the arc from looping appreciably into it and cooling the ionised gas carried through it by the air to a degree sufiicient to prevent the are restriking out side the chute 12 beyond the barrier 18.

The efiect of the air flow is to assist the rapid deionisation of the gas columns previously constituting the various succeeding arc paths 123, and in addition by scavenging and cooling to prevent the re-establishment of the arc across the opening contacts. This re-establishment is further prevented by the air pressure built up in the interior of the arc chute.

The are runner 16 is directly connected to its associated contact 10. However, the moving contact 11 is spaced from its runner 17 by a small air gap 23, across which a small series arc will form when the main arc has been transferred from the contactilt to the runner 17. Such transfer is assisted by the construction of the moving contact H, which is slotted and provided with a small integral finger 24 extending parallel to its length but pointing outwards towards the end of the associated runner 17. Thus the electrical field due to the charged finger 24 tends to drive the root of the main arc towards the runner 17.

in the embodiment of Figures 2 to 4, a high-voltage circuit-breaker is provided with an arc chute 33 built up from a number of individual chute elements or chambers which are arranged around the path of the movable contact and which communicate with one another.

In this embodiment, air from a reservoir or other source is supplied to one end of a tubular insulator 31 whose other end is closed by the metal bottom plate 32 of the associated arc chute assembly 36. Through a close-fitting central hole in this bottom plate a metal tube 33 extends from the bore of the insulator 31 into the interior of the arc chute assembly 30 and forms the moving contact of the circuit-breaker, a cooperating fixed contact 34 being carried by a metal top plate 35 of the assembly which is spaced from the bottom plate 32, one circuit-breaker terminal 36 being attached to the top plate. The moving contact 33 can be totally withdrawn longitudinally from the fixed contact 34 into the interior of the tubular insulator 31 to effect contact separation. The portion of the moving contact 33 which lies in the insulator 31 when in the closed position is provided with perforations 37 to allow compressed air to flow through its wall into its interior, and thence through its open mouth 38 into the interior of the arc chute assembly 30 between the top and bottom plates 35 and 32. The insulator 31 carries an internal metal contact sleeve 39 through which the moving contact passes and to which the other circuit-breaker terminal 4%) is electrically connected. A further contact sleeve 41 makes electrical connection between the moving contact 33 and the bottom plate 32, the latter carrying an associated arc runner 42 which extends radially outwards along the inside surface of the bottom plate as will be described below.

Between the bottom plate 32 and top plate 35 of the assembly is mounted a stack of circular discs 44 of insulating material having coaxial central circular holes 45 which lie in register in the stack to form a central bore 46 through which the moving contact 33 extends towards the fixed contact 34. As shown in Figures 3 and 4, each disc 44 is also formed with a fan-shaped aperture 47 of about 30 angular extent whose narrow inner end communicates with the central hole 45 and which extends radially outwards towards the periphery of the disc; the aperture 47 does not however reach the periphery of the disc, but a small peripheral bridge 48 extends across to close the wide end of the aperture 47. This bridge 48 is formed on its upper and lower surfaces with a series of radial grooves 49.

The arrangement of the stack of discs 44 is such that the fan-shaped apertures 47 are orientated in helical formation around the axis of the stack, each aperture overlapping that below it by only a few degrees so that a narrow radial slot 5% (Figure 4) remains to provide communication between adjacent apertures 47. This is illustrated in Figures 3 and 4, of which the former is an exploded perspective view of four of the discs 44 in their relative orientation, whilst the latter shows the same four discs assembled one on another to form a part of the stack. Each aperture 47, bounded at top and bottom by the surfaces of the adjacent discs 44, provides a chamber constituting one of the arc chute elements of the assembly 31 The arcing runner 42 associated with the loving contact extends radially into the lowest chamber 47, whilst a second arcing runner 51 connected to the fixed contact 34 extends along the inner surface of the A. top plate 35 into the uppermost chamber 47. Thus, a prolonged helical path is provided between the arcing runners 42 and 51 through the inter-communicating chambers 47, into which path the arc may be driven transversely by the air flow for elongation and extinction.

As 1n the previous embodiment, the vent area provided by the radial grooves 49 in the bridge pieces 48 is so proportioned to the cross-sectional area of the tubular insulator 31 that air pressure will be developed inside the arc chute chambers 47 and the central bore 46, with most of the pressure drop taking place across the radial grooves 49 which constitute the vents.

On operation of the circuit-breaker, the air flow is first established through the insulator 31 and moving contact 33 to build up air pressure inside the arc chute assembly 39. The moving contact tube 33 now begins to withdraw, drawing an are between the contacts 33 and 34. The air flow, wh1ch lS radially outwards through the fan-shaped chambers 47 and through the radial grooves 49 in the orrdging pieces 48 of the discs 44, carries the arc towards the surface of the central bore 46 of the stack of discs, the upper arc root transferring to the arc runner 51 associated with the fixed contact and the lower arc root running on the outer surface of the moving contact 33. The radial air flow now carries the are successively into the successive fan-shaped chambers 47 so as to follow the helical path of these chambers, thus extending the length of the arc and cooling it. If arcing continues for a sufiicient time before extinction, the arc will eventually extend throughout the complete helical path between the upper and lower runners 51 and 42 and will be pressed by the air flow against the vented bridge pieces 48 formin the outer ends of the chambers 47. D

The are will be extinguished when partly or fully lengthened, depending on circumstances, and the recovery voltage will then be impressed across the chute structure between the top and bottom plates 34 and 32. The resultant electrical stressing is greatly reduced by the final movement of the moving contact 33 which withdraws completely through the bottom plate 32 into the air duct insulator 31. The air flow can be cut off at a suitable time after arc extinction.

In both the embodiments described and illustrated the transfer and lengthening of the arc in the chute or chutes is effected solely by the air flow, which at no time impinges on the arc in a direction along the length of the arc durlng the lengthening operation. In neither case is the transfer effected with the aid of any auxiliary magnetic means such as blow-out coils or iron plates.

Wh1lst the air supply has been described as being derived from a reservoir of compressed air, it will be realised that in either arrangement the air flow could be generated by means of the contact-spring mechanism of the circuit-breaker.

What we claim as our invention and desire to secure by Letters Patent is:

1. A high-voltage electric circuit-breaker of the airbreak type including separable contacts between which the arc is initiated, an arc chute into which the arc is transferred and in which it is lengthened, a porous insulating barrier in the arc chute, the barrier being permeable by a current of air but impenetrable by the arc, and means for producing a current of air moving through the arc chute transversely to the arc and through the barrier transversely to its upstream surface, whereby the lengthened arc is held longitudinally against the said upstream surface of the barrier by the said air current passing through the barrier and is thereby cooled, said are chute including several separate arc chute chambers arranged in series, said chambers being arranged radially to and in helical disposition around the axis of a central passage in which the arc is initially drawn, the chambers communicating with one another to provide an elongated helical spiral path into which the arc is driven by the radial flow of air outwardly from the central passage.

2. A circuit-breaker as claimed in claim 1 in which the arc chute comprises a stack of insulating laminations provided with registering central apertures which constitutes the said central passage, each lamination being also formed with a segmental aperture constituting an arc chute chamber communicating with the central aperture, the segmental apertures in successive laminations being arranged in helical formation around the axis of the central passage.

3. A circuit-breaker as claimed in claim 2 in which the segmental opertures in adjacent laminations overlap slightly so as to communicate with one another through a narrow radial slot formed by the overlap.

4. A circuit-breaker as claimed in claim 3 in which each segmental aperture is closed at its outer end by an arcuate bridge portion of the lamination, the bridge portion being formed with radial grooves in its upper and/ or lower surfaces and constituting the means for constrain- 5 ing the arc to remain transverse to the air stream.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,147,430 Ellis Feb. 14, 1939 2,160,681 Sandin May 30, 1939 2,272,380 Ludwig et a1. Feb. 10, 1942 2,345,724 Baker et a1. Apr. 4, 1944 2,598,546 Houst. May 27, 1952 

